The principal aim is to isolate and characterize cell surface materials which are associated with human malignant lymphoproliferative disorders. Cultured as well as non-cultured malignant human cells are used to isolate the leukemia-lymphoma associated antigens (LLA). We are using both baboon and rabbit antisera to leukemic cells in three different procedures to detect LLA on cell surface: 1) conventional C'-dependent cytotoxicity test, 2) 125I-antibody binding assay, and 3) quantitative absorption test. The results showed that certain LLA which were not detected by the conventional C'-dependent cytotoxicity test were detected by the latter two procedures. The detected LLA were isolated from radiolabeled cells by detergent-solubilization and specific immunoprecipitation. The immunoprecipitates were solubilized and analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The use of cultured leukemic cells will allow us to isolate the LLA in quantities large enough to prepare strong and specific heteroantisera to LLA and, further, allow us to feed the cells with radiolabeled amino acids so that we can isolate radiolabeled LLA. The radiolabel marker on LLA will greatly facilitate chemical characterization, especially the amino acid sequence determination of LLA.